1. Field of the Invention
The present invention relates to an exposure device, and more particularly to the exposure device that is used for the optical system with a movable mirror to be used in the copying apparatus etc.
2. Description of the Prior Art
Generally, in copying apparatus such as an electrophotographic copying apparatus, an image recording is made in such a manner that the light from a light source is irradiated the surface of an original placed on an original glass plate, and the reflected light therefrom is led to the surface of a charge-retaining member such as a photosensitive substance through the reflection made by the optical system composed of a mirror etc., and thus an electrostatic latent image is formed on the surface of said charge-retaining member. As an aforesaid image recording method, there have generally been known a system wherein the original glass is stationary and the optical system is movable, and alternately a system wherein the optical system is stationary and the original glass plate is movable.
The present invention relates to an exposure device wherein the image recording is effected by the former movable optical system, and the image recording system of said system will be explained, referring to the drawings.
FIG. 1 is a schematic view of a well-known exposure device wherein the optical system moves. In the FIG. 1, the numeral 1 is an original placed on a transparent glass 2 of the original glass plate with its imaging surface downward and irradiated by the illumination lamp 3, the reflected light from said imaging surface forms the light image on the surface of the photosensitive member 9 through the movable mirrors 4, 5 and 6, a fixed mirror 7 and a lens 8 for image formation.
Next, operation of the optical system thus composed will be explained. First, after an illumination lamp 3 is lit, the first mirror 4 that is arranged so that it can move together with said illumination lamp 3 travels in the direction of an arrow at a speed V in parallel with the original. Simultaneously with this travel of the first mirror 4, the second mirror 5 and the third mirror 6 also travel at a speed of 1/2 V in the same direction (the direction of an arrow) in parallel with the original.
Thus, the entire surface of the original is optically scanned and total reflected light from the image area of said original is led onto the surface of the photosensitive member 9 as mentioned above and concurrently with this, the surface of the photosensitive member 9 also rotates at the same speed V as for said first mirror 4, therefore, a said reflected light is image-wise projected onto the surface of the photosensitive member 9 same as an image of the original, and an electrostatic latent image is precisely formed on the surface of the photosensitive member 9.
In the movable optical system as described above, the second mirror 5 and the third mirror 6 move at a half the speed of the first mirror 4 and therefore, said second mirror 5 and third mirror 6 are mounted on a frame in one body and usually move along a guide rail provided on a driving side of said frame being pulled by a wire.